University of Twente Student Theses


Efficient query evaluation on probabilistic XML data : derived from a glue process with skeleton & flesh

Stapersma, Paul (2012) Efficient query evaluation on probabilistic XML data : derived from a glue process with skeleton & flesh.

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Abstract:In many application scenarios, reliability and accuracy of data are of great importance. Data is often uncertain or inconsistent because the exact state of represented real world objects is unknown. A number of uncertain data models have emerged to cope with imperfect data in order to guarantee a level of reliability and accuracy. These models include probabilistic XML (P-XML) {an uncertain semi-structured data model{ and U-Rel {an uncertain table-structured data model. U-Rel is used by MayBMS, an uncertain relational database management system (URDBMS) that provides scalable query evaluation. In contrast to U-Rel, there does not exist an efficient query evaluation mechanism for P-XML. In this thesis, we approach this problem by instructing MayBMS to cope with P-XML in order to evaluate XPath queries on P-XML data as SQL queries on uncertain relational data. This approach entails two aspects: (1) a data mapping from P-XML to U-Rel that ensures that the same information is represented by database instances of both data structures, and (2) a query mapping from XPath to SQL that ensures that the same question is specified in both query languages. We present a specification of a P-XML to U-Rel data mapping and a corresponding XPath to SQL mapping. Additionally, we present two designs of this specification. The first design constructs a data mapping in such way that the corresponding query mapping is a traditional XPath to SQL mapping. The second design differs from the first in the sense that a component of the data mapping is evaluated as part of the query evaluation process. This offers the advantage that the data mapping is more efficient. Additionally, the second design allows for a number of optimizations that affect the performance of the query evaluation process. However, this process is burdened with the extra task of evaluating the data mapping component. An extensive experimental evaluation on synthetically generated data sets and real-world data sets shows that our implementation of the second design is more efficient in most scenarios. Not only is the P-XML data mapping executed more efficient, the query evaluation performance is also improved in most scenarios.
Item Type:Essay (Master)
Faculty:EEMCS: Electrical Engineering, Mathematics and Computer Science
Subject:54 computer science
Programme:Computer Science MSc (60300)
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